Data transfer device, semiconductor integrated circuit, and microcomputer

ABSTRACT

It is aimed at improving the efficiency of data transfer processing and the concurrent data processing on a central processing unit. A data transfer device can independently request a bus access right and output an address to a first bus (IBUS) and a second bus (PBUS). It is possible to solve the state of competing for the bus access right between both buses. While the bus access right of one bus is granted for reading or writing, the bus access right of the other bus can be released. When the data transfer device releases the bus access right for the first bus, a central processing unit can process data. In response to one data transfer start request, the bus access right is requested for one bus and the other bus, There is not used a sequence of requesting the bus access right in response to different data transfer requests for respective buses. It is possible to simplify a handshake sequence of a data transfer request and its acknowledgment.

BACKGROUND OF THE INVENTION

The present invention relates to a data transfer device. Morespecifically, the present invention relates to a semiconductorintegrated circuit and a microcomputer containing the data transferdevice, e.g., to a technology effectively used for a single-chipmicrocomputer having a high-speed external input/output interfacecircuit.

A single-chip microcomputer comprises functional blocks such as acentral processing unit (CPU) as a main component, ROM (read-onlymemory) for storing programs, RAM (random access memory) for storingdata, and an input/output circuit for data input and output. Thesefunctional blocks are formed on a single semiconductor substrate.

There is available a single-chip microcomputer that contains a directmemory access controller (DMAC) and is capable of data transferindependently of the CPU (see patent document 1). An interrupt requestcan activate the DMAC capable of repeat mode and block transfer mode. Ina printer system, for example, the DMAC is suitable for controllingstepping motors, controlling printout data on a printer, and storingreceived data in memory. Such example is capable of transferring up toeight channels of data. Since the DMAC transfers data independently ofthe CPU but shares a bus with the CPU, a bus cycle needed for the DMACdata transfer stops CPU operations. That is to say, in response to asingle activation request, the DMAC obtains a bus access right andoccupies the bus between two bus cycles for reading and writing. Whenbyte data is transferred from the RAM to the input/output circuit toincrement transfer origin and destination addresses, the DMAC occupiesthe bus for six states of data transfer including two states for RAMaccess, three states for input/output circuit access, and one state fora dead cycle in the above-mentioned example. It should be noted that onestate signifies once cycle of reference clock for the single-chipmicrocomputer or the semiconductor integrated circuit device.

When the DMA controller is connected to an external bus for themicrocomputer, it is possible to perform operations of internal busessuch as a ROM lead for the CPU in parallel with external bus transfersuch as transferring received data to the memory by means of theexternal DMA controller. However, releasing the external bus accessright causes a delay in recognizing an acknowledge signal or a requestsignal while the bus access right is exchanged. There is generated atime interval during which the microcomputer and the external DMAcontroller do not use the bus so as to prevent both from colliding witheach other on the bus. This easily generates an overhead irrelevant toactual operations. Overheads, if occurring before and after a singledata transfer, are not negligible in comparison with the time requiredfor an actual data transfer. If a general-purpose DMA controller isused, it also provides unnecessary functions, unfavorable to costeffectiveness. Though it is possible to develop a DMA controlleroptimized for each system, this is apt to be disadvantageous tomanufacturing costs and the like spent for the microcomputer and adifferent LSI chip.

The above-mentioned application (see patent document 2) by the inventorsuses the on-chip configuration for an external bus DMAC that allows themicrocomputer to transfer data on the external bus, enabling concurrentoperations of the external bus and the microcomputer's internal bus.Concurrent operations are made available between the external bus DMAC'sdata transfer on the external bus and internal bus master's operationson the internal bus such as execution of instructions by the CPU usingthe internal bus. It is possible to simultaneously enable data transferby the external bus DMAC on the external bus and instruction executionby the CPU using the internal bus, thus improving the microcomputer'sthroughput. Data can be transferred on the external bus withoutdegrading the CPU throughput.

In short, the DMAC represented in the above-mentioned patent documents 1and 2 is connected as a bus master to a single bus (either the internalbus or the external bus). The DMAC uses that bus to transfer data suchas reading and writing. Accordingly, the DMAC continuously occupies thebus access right of the single bus during operations of accessing asource address and destination address.

By contrast, patent document 3 describes an example of providing buffermemory capable of reading or writing via interfaces providedcorrespondingly to two different data processing devices. There isprovided the data transfer function for exchanging data between theabove-mentioned buffer memory and the data processing devicescorresponding to the two interfaces. In this case, data is transferredfrom peripheral processing devices to the buffer memory via the firstinterface. Further, data is transferred from the buffer memory to themain memory via the second interface. These two types of data transfersare performed independently. A request to transfer data is also issuedindependently.

Patent document 1

Japanese Unexamined Patent Publication No. Hei 5(1993)-307516A

Patent document 2

Japanese Unexamined Patent Publication No. 2000-235560

Patent document 3

Japanese Unexamined Patent Publication No. Hei 5(1993)-2557

SUMMARY OF THE INVENTION

The inventors examined improvement of the total throughput of themicrocomputer and the like from the viewpoint of data transfer control.With an increasing demand for miniaturization of application systems andadvancement in micro-fabrication of semiconductor integrated circuits,various interface circuits are being integrated into the microcomputer.Examples are a USB (universal serial bus) interface and an MMC(multimedia card) interface. Generally, since data input from suchinterface is temporarily stored in buffer RAM, the DMAC is used totransfer data from the interface to the buffer RAM. There is anincreasing number of application devices that handle audio data andimage data, necessitating a large amount of data to be transferred at ahigh speed. For example, the USB data transfer rate is 480 Mbps. If theCPU cannot use the bus to prevent a program from being executed during aperiod of data transfer, making it impossible to control the entiresystem and causing problems. In short, the USB interface or the like isused to receive a large amount of data too fast to permit interruptiveprocesses by the CPU. On the contrary, a low interface speedsufficiently allows the CPU to interrupt at any time. Depending onsituations, the CPU may need to process data stored in the buffer RAM.When the buffer RAM uses synchronous DRAM that is suitable for continuesaccesses, it may be possible to provide faster processing bytransferring the predetermined amount of data to the internal RAM,processing the data, and then rewriting the data to the buffer RAMrather than allowing the CPU to sequentially read and write data. Inthis case, the DMAC needs to ensure fast data transfer between thebuffer RAM and the internal RAM. It is necessary to prevent a delay inthe CPU processing time if the processed data is transferred or new datais input concurrently.

As represented in the above-mentioned patent documents 1 and 2, however,the DMAC is connected as a bus master to the single bus (one of theinternal bus and the external bus) and uses that bus to transfer datafor reading or writing. This delays processing of the CPU that sharesthe single bus. According to the technology of patent document 3,independent data transfer requests are issued to independently transferdata to and from the buffer memory via two different interfaces. Thisincreases a time interval for a handshake sequence between the datatransfer request and acknowledgment. It is considered to be difficult toimprove effectiveness between data transfer processing and dataprocessing by the CPU.

It is an object of the present invention to improve the efficiency ofdata transfer processing and concurrent data processing by the centralprocessing unit.

It is another object of the present invention to provide a data transferdevice, a semiconductor integrated circuit, and a microcomputer capableof concurrently enabling processing mainly comprising reading programsby the central processing unit and data transfer processing betweenvarious interface circuits and buffer memory and capable of improvingthe efficiency of both types of processing to be paralleled.

These and other objects and novel features of the invention may bereadily ascertained by referring to the following description andappended drawings.

The following outlines major aspects of the present invention disclosedin this application.

[1] A data transfer device according to the present invention isconnected to a first bus (IBUS) and a second bus (PBUS) and transfersdata between these buses. The device can independently request a busaccess right and output an address to the first and second buses. Thedevice requests a bus access right of one bus for reading and requests abus access right of the other bus for writing in response to one datatransfer start request.

It is possible to independently request the bus access right and outputaddresses to the first and second buses, making it possible to solve thestate of competing for the bus access right between both buses. Whilethe bus access right of one bus is granted for reading or writing, thebus access right of the other bus can be released. When the centralprocessing unit is connected to either the first or second bus,releasing the bus access right by the data transfer device enables dataprocessing for the central processing unit.

In response to one data transfer start request, the bus access right isrequested of one bus and the other bus, not using a sequence ofrequesting the bus access right in response to different data transferrequests for respective buses. It is possible to simplify a handshakesequence of a data transfer request and its acknowledgment andcontribute to effective data transfer processing and data processing bya central processing unit.

As a preferred mode of the present invention, it is preferable torequest a bus access right of the one bus and request a bus access rightof the other bus at different timings. For example, a bus access rightis requested of the one bus at a predetermined timing for readoperations of the other bus granted a bus access right.

As a preferred mode of the present invention, the data transfer devicehas a plurality of data transfer channels and a control register tospecify data transfer channel operations. The control register has atransfer request generation source specification area for definingcorrespondence between a data transfer channel to receive a transferrequest and a transfer request generation source; a source busspecification area for defining correspondence between a data transferchannel and a transfer source bus; and a destination bus specificationarea for defining correspondence between a data transfer channel and atransfer destination bus.

[2] A semiconductor integrated circuit (1) according to a first aspectof the present invention comprises: a first bus (IBUS); a second bus(PBUS); a data transfer device (5) to transfer data between the firstand second buses; a central processing unit (3) connected to the firstbus; and program storage memory (7) which stores a control program forthe central processing unit and is connected to the first bus. The datatransfer device can independently request a bus access right and outputan address to the first and second buses. The device requests a busaccess right of one bus for reading and requests a bus access right ofthe other bus for writing at a different timing in response to one datatransfer start request. The central processing unit is capable of busaccess using the first bus in parallel with bus access using the secondbus by means of the data transfer device. Likewise, as mentioned above,this makes it possible to not only concurrently allow data transferprocessing and data processing by a central processing unit, but alsoimprove the efficiency of both processing.

A semiconductor integrated circuit according to a second aspect of thepresent invention comprises: a first bus; a second bus; a data transferdevice to transfer data between the first and second buses; a centralprocessing unit connected to the first bus; and a bus control means (11)for the first and second buses. The data transfer device canindependently request a bus access right and output an address to thefirst and second buses. The device requests a bus access right of onebus for reading and requests a bus access right of the other bus forwriting at a different timing in response to one data transfer startrequest. The bus control means is capable of arbitration of bus accessright requests and bus control for the first and second busesindependently. Likewise, as mentioned above, this makes it possible tonot only concurrently allow data transfer processing and data processingby a central processing unit, but also improve the efficiency of bothprocessing.

A semiconductor integrated circuit according to a third aspect of thepresent invention comprises: a first bus(IBUS); a second bus(PBUS); athird bus(EXBUS, EXIFBUS); a central processing unit(3) connected to thefirst bus; program storage memory which stores a control program for thecentral processing unit and is connected to the first bus; and a datatransfer device(5) capable of data transfer between the second and thirdbuses. The data transfer device can independently request a bus accessright and output an address to the second and third buses. The devicerequests a bus access right of one bus for reading and requests a busaccess right of the other bus for writing at a different timing inresponse to one data transfer start request. The central processing unitis capable of bus access using the first bus in parallel with bus accessusing the second or third bus by means of the data transfer device.Likewise, as mentioned above, this makes it possible to not onlyconcurrently allow data transfer processing and data processing by acentral processing unit, but also improve the efficiency of datatransfer processing in terms of a handshake sequence between a transferrequest and acknowledgment.

As a preferred mode of the present invention, there is provided a buscontrol means (11) for the first through third buses. The bus controlmeans is capable of arbitration of bus access right requests and buscontrol for the first through third buses independently. Further, thecentral processing unit can access the second or third bus from thefirst bus via the-bus control means.

[3] A microcomputer according to the present invention comprises: afirst bus(IBUS); a second bus(PBUS); a third bus(EXIFBUS, EXBUS); acentral processing unit (3) connected to the first bus; program storagememory (7) which stores a control program for the central processingunit and is connected to the first bus; and a data transfer device (5)capable of data transfer between any two of the first through thirdbuses. The data transfer device can independently request a bus accessright and output an address to the first through third buses. The devicerequests a bus access right of one bus for reading and requests a busaccess right of the other buses for writing at a different timing inresponse to one data transfer start request. Likewise, as mentionedabove, this makes it possible to not only concurrently allow datatransfer processing and data processing by a central processing unit,but also improve the efficiency of both processing.

As a preferred mode of the present invention, the central processingunit performs a bus access using the first bus in parallel with busaccess using the second or third bus by means of the data transferdevice. This is because the central processing unit's program memory isconnected to the first bus. Further, there is provided a bus controlmeans for the first through third buses. The bus control means iscapable of arbitration of bus access right requests and bus control forthe first through third buses independently. The central processing unitcan access the second or third bus from the first bus via the buscontrol means.

For example, the bus control means has first to third bus control logiccircuits. The first bus control logic circuit arbitrates bus requestsfrom bus masters such as the central processing unit and the datatransfer device to the first bus and grants a bus access right inaccordance with predetermined priorities. The first bus control logiccircuit checks an address output from the bus master to determinewhether the address corresponds to the first, second, or third bus. Whenthe address corresponds to the first bus, the first bus control logiccircuit controls bus cycles of the first bus. When the addresscorresponds to the second bus, the first bus control logic circuitpasses control to the second bus control logic circuit and waits untilthe bus cycle is complete. When the address corresponds to the thirdbus, the first bus control logic circuit likewise passes control to thethird bus control logic circuit and waits until the bus cycle iscomplete.

The second bus control logic circuit centrally controls accesses to thesecond bus from the first bus' bus masters such as the centralprocessing unit and the like and from the data transfer device inaccordance with specifications such as the bus width specific to theaddress and the number of access states. At this time, the data transferdevice outputs addresses and bus commands as special signals for usingthe second bus. Further, the second bus control logic circuit arbitratesaccesses to the second bus from the first bus' bus masters such as thecentral processing unit and the like and bus access right requests forthe second bus from the data transfer device.

The third bus control logic circuit has a divided address space and iscapable of setting bus specifications such as memory types and thenumber of access states. The third bus control logic circuit centrallycontrols accesses to the third bus from the first bus' bus masters suchas the central processing unit and the like and from the data transferdevice. At this time, the data transfer device outputs addresses and buscommands as special signals for using the third bus. Further, the thirdbus control logic circuit arbitrates access requests for the third busfrom the first bus' bus masters such as the central processing unit andthe like and access requests from the data transfer device and the otherexternal bus modules.

As a preferred mode of the present invention, the data transfer devicehas a plurality of data transfer channels and a control register tospecify data transfer channel operations. The control register has atransfer request generation source specification area for definingcorrespondence between a data transfer channel to receive a transferrequest and a transfer request generation source; a source busspecification area for defining correspondence between a data transferchannel and a transfer source bus; and a destination bus specificationarea for defining correspondence between a data transfer channel and atransfer destination bus. A central processing unit can access thecontrol register.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a microcomputer according to an example ofthe present invention;

FIG. 2 shows an address map exemplifying the address space of the CPU;

FIG. 3 is a block diagram exemplifying details of a DMAC;

FIG. 4 exemplifies details of a register configuration for one datatransfer channel of the DMAC;

FIG. 5 is a state transition diagram of data transfer control by theDMAC;

FIG. 6 is a timing chart for the first example of using the DMAC;

FIG. 7 is a timing chart for the second example of using the DMAC; and

FIG. 8 is a block diagram exemplifying a microcomputer system using themicrocomputer for printer control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a microcomputer according to an example of the presentinvention. Though not subject to special requirements, a microcomputer 1in FIG. 1 is formed on a semiconductor substrate such as silicon singlecrystal by means of the CMOS integrated circuit fabrication technology.

The microcomputer 1 comprises: a central processing unit (CPU)3; a DMAcontroller (DMAC) 5; read-only memory (ROM) 7; random access memory(RAM) 9; a bus controller (BSC) 11; an input/output interface 13; aperipheral function circuit 15; and an input/output port (IOP) 17.Though not shown in FIG. 1, the microcomputer 1 further comprisesfunctional blocks or modules such as an interrupt controller, a clockoscillator, and the like. The peripheral function circuit 15 comprises,for example, a timer, a pulse output circuit, a serial communicationinterface (SCI), and an A/D converter (A/D).

The CPU 3 mainly functions and reads instructions mainly from the ROM 7for operations to read or write data to the RAM 9 as a working dataarea. The program memory for the CPU 3 maybe not only the ROM 7, butalso cache memory. Likewise, the cache memory can be also used for datamemory of the CPU 3.

The DMAC 5 shares a first I bus (internal bus) IBUS with the CPU 3 andcan transfer data instead of the CPU 3. The peripheral function circuit15 and the input/output interface circuit 13 request to start datatransfer in response to transfer request signals treq-io and treq-petypically represented by the DMAC 5. The DMAC 5 transfers data inresponse to the start request and then returns typical transferacknowledge signals tack-io and tack-pe to clear the initiation factor.The interrupt controller may be used to determine or clear initiationfactors.

The microcomputer 1 has the internal bus (I bus) IBUS as the first bus,a peripheral bus (P bus) PBUS as the second bus, an external interfacebus (EXIFBUS), and an external bus (EX bus) EXBUS leading to the outsideof the chip. These buses are used to connect the internal circuitmodules. The buses include not only an address bus and a data bus, butalso bus commands (or read signal, write signal, and bus size signal)and a ready signal (or a wait signal). The microcomputer 1 as thesemiconductor integrated circuit has an internal line Linr as theexternal bus EXBUS. The internal line Linr leads to an external terminalTML connected to a bus signal line outside the chip. Strictly speaking,a third bus provided for the microcomputer 1 as the semiconductorintegrated circuit corresponds to the above-mentioned internal line Linrfor the external interface bus EXIFBUS and the external bus EXBUS. Inthis specification, these buses are also simply referred to as theexternal bus EXBUS for convenience.

The internal bus IBUS is directly connected to the CPU 3 and the otherinternal bus masters. The memories 7 and 9 are also connected to theinternal bus IBUS for fast access to memories. The memories 7 and 9 areaccessed in the 1 state.

The peripheral bus PBUS connects with the input/output interface circuit13, the peripheral function circuit 15, and an internal I/O registerincluded in an input/output port 17. Separating the internal bus IBUSfrom the peripheral bus PBUS decreases loads on the internal bus IBUSmainly used for reading programs by the CPU 3 to accelerate processing.When the peripheral bus PBUS is not used, its state is maintained forconveniently saving the power consumption. The CPU 3 accesses theinternal I/O register connected to the peripheral bus PBUS via theinternal bus IBUS and the bus controller 11. The internal I/O registeris accessed in the 2-state.

The internal bus IBUS interfaces with the external bus EXBUS via theexternal interface bus EXIFBUS and an external bus buffer circuit (BUF)27 under control of the bus controller 11. Though not subject to specialrequirements, the external bus buffer circuit (BUF) 27 is included inthe input/output port (IOP) 17. The internal bus IBUS interfaces withthe peripheral bus PBUS under control of the bus controller 11.

The bus controller 11 controls the buses IBUS, PBUS, and EXBUS.Corresponding to each bus, the bus controller 11 has an internal busarbiter (I-ARB) 20, a peripheral bus arbiter (P-ARB) 21, an external busarbiter (EX-ARB) 22, an internal bus controller (I-BSC) 23, a peripheralbus controller (P-BSC) 24, an external bus controller (EX-BSC) 25, and arefresh timer (REF) 26. The bus controller 11 controls the external busEXBUS via the external interface bus EXIFBUS and the external bus buffercircuit (BUF) 27.

The internal bus IBUS is connected to the DMAC 5, the ROM 7, the RAM 9,the external bus buffer circuit (BUF) 27, and the bus controller 11.Here, the CPU 3 and the DMAC 5, as internal bus masters, can use theinternal bus IBUS. The DMAC 5 requests the bus access right based on abus access right request signal dmareq-i. The CPU 3 requests the busaccess right based on a bus access right request signal cpureq-i. Whenthe bus access right request signals dmareq-i and cpureq-i are issued torequest the bus access right, the internal bus arbiter 20 performs anecessary arbitration according to a predetermined priority and providesthe CPU 3 or the DMAC 5 with the bus access right. Permission of the busaccess right is notified by bus access right acknowledge signalscpuack-i and dmaack-i. In this manner, the CPU 3 and the DMAC 5exclusively use the internal bus IBUS. The internal bus master, whenprovided with the bus access right, outputs an address signal and a buscommand to the internal bus IBUS for accessing the bus. The internal buscontroller 23 decodes the address signal output from the CPU 3 to theinternal bus IBUS. When the access is made to a circuit module on theinternal bus IBUS such as the ROM 7, the internal bus controller 23controls the bus using the internal bus IBUS. When the access is made toa circuit module on the peripheral bus PBUS such as the internal I/Oregister of the peripheral function circuit 15, the internal buscontroller 23 activates the peripheral bus controller 24 to deactivatethe bus ready signal on the internal bus IBUS and allow the CPU 3 towait. Further, the internal bus controller 23 requests the peripheralbus arbiter 21 for the bus access right to the peripheral bus. When thebus access right request is acknowledged, the internal bus controller 23controls the peripheral bus PBUS. When the access is made to a circuitmodule on the external bus EXBUS, the internal bus controller 23activates the external bus controller 25 to deactivate the bus readysignal on the internal bus IBUS and allow the CPU to wait. Further, theinternal bus controller 23 requests the external bus arbiter 22 for thebus access right to the external bus EXBUS. When the bus access rightrequest is acknowledged, the internal bus controller 23 controls theexternal bus EXBUS.

The peripheral bus PBUS is connected to the bus controller 11, the DMAC5, the input/output interface circuit 13, the peripheral functioncircuit 15, and an IOP 17. The peripheral bus controller 24 controls theperipheral bus PBUS. The DMAC 5 functions as a peripheral bus masterconnected to the peripheral bus PBUS. The peripheral bus arbiter 21arbitrates the bus access right to the peripheral bus PBUS. The DMAC 5outputs a bus access right request signal dmareq-p to the peripheral busarbiter 21. The peripheral bus arbiter 21 returns a bus access rightacknowledge signal dmaack-p to the DMAC 5. The peripheral bus arbiter 21arbitrates a request for the bus access right from the DMAC 5 and arequest to use the bus from the internal bus controller 23 due to theaccess from the CPU 3 according to predetermined priorities andacknowledges the bus access right to either. When the DMAC 5 is grantedthe bus access right, the DMAC 5 outputs an address signal and a buscommand to the peripheral bus PBUS for accessing the bus. When theacknowledgment is made for the request from the internal bus controller23 to use the bus due to the access from the CPU 3, the peripheral buscontroller 24 controls the bus using the peripheral bus IBUS. Asmentioned above, the internal bus arbiter 20 once arbitrates the busaccess right of the CPU 3. When the CPU 3 granted the bus access rightis to access the peripheral bus PBUS, the peripheral bus access right isto be requested via the internal bus controller 23. In other words, theCPU 3 does not request the peripheral bus access right while using theinternal bus IBUS. While the CPU 3 uses the internal bus IBUS, the DMAC5 is ensured to concurrently read or write data on the peripheral busPBUS.

Though not subject to special requirements, the external bus EXBUS isconnected to the bus controller 11 and the DMAC 5 via the external busbuffer circuit (BUF) and the external interface bus EXIFBUS. In FIG. 1,the external bus EXBUS connects with a synchronous DRAM (SDRAM) 28representatively indicated as a chip independent of the microcomputer 1.The external bus controller 25 controls the external bus EXBUS. When theDRAM is connected to the external bus EXBUS, the external bus controller25 also controls address multiplexing and the like. External bus masterscapable of using the external bus EXBUS include the CPU 3, the DMAC 5,the refresh timer 26, and another external bus master (not shown). Theexternal bus arbiter 22 arbitrates bus access right requests from thesebus masters. The DMAC 5 issues dmareq-ex as a bus access right requestsignal and receives dmaack-ex as a bus access right acknowledge signal.An exreq-ex signal supplies bus access right request signal BREQ fromthe external bus master. The corresponding bus access right acknowledgesignal exack-ex is supplied as bus access right acknowledge signal BACKto the external bus master. When the DMAC 5 is granted the bus accessright, the DMAC 5 outputs an address signal and a bus command to theexternal bus EXBUS from the external interface bus EXIFBUS for accessingthe external bus. When the refresh timer 26 is granted the bus accessright, the external bus controller 25 outputs an address signal and abus command to the external bus EXBUS from the external interface busEXIFBUS for bus access to refresh the SDRAM 28 on the external bus. Whenthe external bus arbiter 22 acknowledges a request to use the bus fromthe internal bus controller 23 due to the access from the internal busmaster, the external bus controller 24 performs bus control using theexternal interface bus EXIFBUS and the external bus EXBUS. As mentionedabove, the internal bus arbiter 20 once arbitrates the bus access rightof the CPU 3. When the CPU 3 is granted the bus access right to accessthe external bus, the CPU 3 requests the external bus access right. Inother words, the CPU 3 does not request the external bus access rightwhile using the internal bus IBUS. When the CPU 3 uses the internal busIBUS, the DMAC 5 and the refresh timer 26 are ensured to access theexternal bus EXBUS or release the bus access right to the external busmaster.

The refresh timer 26 generates a refresh request at a predetermined timeinterval. When granted the external bus access right, the refresh timer26 performs CAS-before-RAS refresh to refresh the SDRAM, for example.When the external bus master is granted the external bus access right,the external bus (address bus, data bus, or control signal) EXBUS ismade to a high impedance state. This enables the external bus master touse the external bus and activates the external bus access rightacknowledge signal BACK to notify it.

As mentioned above, the DMAC 5 can output a bus access right request tothe internal bus IBUS, the peripheral bus PBUS, and the external busEXBUS independently. Depending on the bus used for data transfer, theDMAC can output internal bus access right request dmareq-i, peripheralbus access right request dmareq-p, and external bus access right requestdmareq-ex to any of the internal bus arbiter 20, the peripheral busarbiter 21, and the external bus arbiter 22, respectively. Whenrequesting the internal bus access right, the DMAC 5 supplies internalbus access right acknowledge signal dmaack-i to confirm theacknowledgment of the internal bus access right. The DMAC 5 then issuesan internal bus command and an address to access the internal bus IBUS.Likewise, when requesting the peripheral bus arbiter 21 for theperipheral bus access right, the DMAC 5 supplies peripheral bus accessright acknowledge signal dmaack-p to confirm the acknowledgment of theperipheral bus access right. The DMAC 5 then issues a peripheral buscommand and an address to access the peripheral bus PBUS. The sameapplies to the external bus.

As mentioned above, the CPU 3 can request the internal bus IBUS for thebus access right and use the peripheral bus PBUS and the external busEXBUS via the internal bus IBUS.

The CPU 3 or the DMAC 5 reads or write data to the ROM 7 and the RAM 9as internal bus slaves or to the functional blocks such as theinput/output interface circuit 13, the peripheral function circuit 15,and the IOP 17 as peripheral bus slaves. According to transfer controldata settings and the like, the CPU 3 defines the DMAC 5 to be aperipheral bus slave capable of reading or writing.

The following outlines the other functions provided for themicrocomputer 1. For example, an interrupt controller (not shown) inputsinterrupt signals output from the functional blocks such as theinput/output interface circuit 13, the peripheral function circuit 15,and the IOP 17 and outputs interrupt request signals to the CPU 3. TheIOP 17 is used together with external bus signals (address bus output,data bus input/output, and bus control signal input/output) andinput/output signals of a timer, a pulse output circuit, and the likeconstituting the peripheral function circuit 15. Though not shown in thefigure, there are further provided a power terminal, a circuit groundterminal, an analog power terminal, an analog ground terminal, a resetinput terminal, a standby input terminal, an interrupt input terminal, aclock input terminal, an operation mode terminal, and the like.

FIG. 2 exemplifies an address space of the CPU 3. Though not subject tospecial requirements, the CPU 3 has the 4-gigabyte address space and isdivided into eight areas. According to settings of the bus controller11, these areas are independently capable of configuring a bus width andthe number of access states. The external bus controller 25 controls anexternal bus space. On the other hand, the ROM 7, the RAM 9, and theinternal I/O register in the microcomputer 1 operate on specific buswidths and access states independently of the setting of the buscontroller 11. As mentioned above, the internal ROM 7 and RAM 9 areconnected to the internal bus IBUS and is subject to read/writeoperations in the 1-state. The internal I/O register is connected to theperipheral bus PBUS and is subject to read/write operations in the2-state.

FIG. 3 exemplifies a block diagram of the DMAC 5. Though not subject tospecial requirements, the DMAC 5 has four data transfer channels. FIG. 3representatively shows one data transfer channel CHN. The DMAC 5 has acontrol circuit 31, a data selector 33, a data buffer 35, an addressselector 37, and an arithmetic unit (AU) circuit 39 in common with eachdata transfer channel. Each data transfer channel CHN of four channelsis provided with a control register DTMR, a destination address registerDAR, a source address register SAR, and a transfer count register TCR tobe described later.

The DMAC 5 inputs a plurality of transfer request signals treqrepresented by treq-io and treq-pe as mentioned above. When performingthe corresponding data transfer, the DMAC 5 outputs a plurality oftransfer acknowledge signals tack represented by tack-io and tack-pe asmentioned above.

As mentioned above, the DMAC 5 is capable of data input/outputindependent of the three buses IBUS, PBUS, and EXBUS. When data istransferred in response to one data transfer start request generated byone transfer request signal, the DMAC 5 requests the bus access right tothe bus corresponding to each of a transfer source address and atransfer destination address at respective timings for reading orwriting data to the bus to be accessed. The DMAC 5 issues the dedicatedbus access right request signals dmareq-i, dmareq-p, and dmareq-ex tothe internal bus arbiter 20, the peripheral bus arbiter 21, and theexternal bus arbiter 22, respectively to request the bus access right ofeach bus arbiter. The DMAC 5 is then notified of acknowledgment of thebus access right by means of the dedicated bus access right acknowledgesignals dmaack-i, dmaack-p, and dmaack-ex. When notified ofacknowledgment of the bus access right, the DMAC 5 generates a buscommand and outputs an address to the bus to be accessed for accessoperations in response to a ready state of the bus ready signal outputfrom the corresponding bus controller. The data transfer channel to beused is set to the control register DTMR of each data transfer channelin correspondence with the transfer request. The bus used for datatransfer is set to the control register DTMR of each data transferchannel. It may be preferable to determine a bus to be used by decodingaddresses predetermined in the source address register SAR and thedestination address register DAR.

The DMAC 5 once stores data read from data bus idb (for IBUS), pdb (forPBUS), or exdb (for EXBUS) of the source bus for which the bus accessright is granted, in the data buffer 35 via the data selector 33. TheDMAC 5 then rewrites that data to data bus idb (for IBUS), pdb (forPBUS), or exdb (for EXBUS) of the destination bus for which the busaccess right is granted, via the data selector 33. In this manner, it ispossible to independently select a bus for reading and a bus forwriting.

The address selector 37 inputs the contents of the source addressregister SAR or the destination address register DAR from an internalbus 40 of the DMAC 5. The address selector 37 then outputs the contentsto address bus iab (for IBUS), pab (for PBUS), or exab (for EXBUS) ofthe bus for which the bus access right is granted.

The arithmetic unit circuit 39 increments or decrements the sourceaddress register SAR and the destination address register DAR anddecrements the transfer count register TCR. The transfer count registerTCR contains an initial value for the number of data transfers ortransfer words.

The control circuit 31 detects the transfer request signal treq toinitiate an operation and controls bus access right requests as well asbus command and address outputs. In addition, the control circuit 31inputs the bus access right acknowledge signal tack and the bus readysignal and concurrently controls bus operations. Though not shown in thefigure, the CPU 3 performs read/write operations as a peripheral businterface for the DMAC 5. For this purpose, the peripheral buscontroller 24 outputs a module select signal, a read signal, a writesignal, low-order bits of an address to the peripheral bus PBUS, andinputs or outputs data to the peripheral bus. In accordance with theseoperations, the control circuit 31 can perform initialization or readsetup data for the registers SAR, DAR, TCR, and DTMR of each datatransfer channel, i.e., one of internal I/O registers.

FIG. 4 exemplifies details of the register configuration of the DMAC 5for one data transfer channel. Though not subject to specialrequirements, the source address register SAR and the destinationaddress register DAR are configured in 32 bits and store transfer sourceand destination addresses. Though not subject to special requirements,these registers can directly specify all areas in the 4-gigabyte addressspace of the microcomputer.

Though not subject to special requirements, the transfer count registerTCR is configured in 16 bits and stores the number of data transfers.The transfer count register TCR is decremented each time data istransferred in response to one start request.

The control register DTMR controls a transfer mode of the DMAC 5 and thelike. Each bit of the DTMR functions as follows.

Bit 15 functions as a DTE bit to permit DMAC operations for the relevantchannel. When the transfer request signal is activated with the DTE bitset to 1, the corresponding data transfer channel starts operating.

Bit 14 is a DEND flag and is set to 1 when the predetermined number oftransfers terminates, i.e., when TCR is reset to 0.

Bit 13 is a DIE bit and allows an interrupt. When both the DIE and DENDbits are set to 1, the CPU 3 is requested to be interrupted. When theDIE bit is set to 1 and the DEND flag is set to 1, the DTE bit is resetto 0. An operation of the data transfer channel is interrupted, awaitinga process by the CPU 3.

Bits 2 through 0 correspond to DTS bits 2 through 0 and specify a sourceof generating a transfer request as a trigger to start the transferoperation. For example, 000 specifies a start request based on inputcompletion of the input/output interface circuit 13; 001 specifies astart request based on output completion of the input/output interfacecircuit 13; 010 specifies a start request based on a first compare matchof the timer; 011 specifies a start request based on a second comparematch of the timer; 100 specifies a start request based on inputcompletion of SCI; 101 specifies a start request based on outputcompletion of SCI; and 110 specifies a start request based on anexternal request.

Bits 9 and 8 correspond to SZ1 and SZ0 bits and specify a size per datatransfer: 01 for a byte; 10 for a word (2 bytes); and 11 for a long word(4 bytes).

Bits 7 and 6 correspond to SM1 and SM0 bits and specify whether toincrement, decrement, or fix the source address register SAR after datatransfer. Resetting the SM1 bit to 0 fixes the source address registerSAR. When the SM1 bit is set to 1, resetting the SM0 bit to 0 incrementsthe source address register SAR; and setting the SM0 bit to 1 decrementsit.

Bits 5 and 4 correspond to DM1 and DM0 bits and specify whether toincrement, decrement, or fix the destination address register DAR afterdata transfer. Resetting the DM1 bit to 0 fixes the destination addressregister DAR. When the DM1 bit is set to 1, resetting the DM0 bit to 0increments the destination address register DAR; and setting the DM0 bitto 1 decrements it.

Bits 3 and 2 correspond to SA1 and SA0 bits and select a bus to be usedas the source address. The bus access right is requested to the internalbus IBUS when the bits are set to 00 or 01; to the peripheral bus PBUSwhen the bits are set to 10; and to the external bus EXBUS when the bitsare set to 11.

Bits 1 and 0 correspond to DA1 and DA0 bits and select a bus to be usedas the destination address. These bits are predetermined in the samemanner as the SA1 and SA0 bits. It is possible to easily determine a busto be used by using the bus specification bits SA1, SA0, DA1, and DA0rather than specifying source and destination addresses.

FIG. 5 exemplifies a state transition diagram of the DMAC 5. This statetransition is implemented by the logic in the control circuit 31 of theDMAC 5.

The DMAC 5 has seven states: state I (idle); state SR (source request);state SA (source address); state SD (source data); state DR (destinationrequest); state DA (destination address); and state DD (destinationdata).

After a reset, the DMAC 5 changes to state I. State I samples a requestsignal to start the DMAC 5. Setting the transfer enable bit of anychannel to 1 detects a request to start the channel. When a plurality ofchannels is started, channel 0 is given the highest priority foroperations.

When the start request causes a predetermined input (dreq=1), the DMAC 5changes to the state SR. The state SR requests the bus access right(breq_s=1) to any of the buses predetermined as a source, i.e., theinternal bus IBUS, the peripheral bus PBUS, and the external bus EXBUS.As mentioned above, the SA1 and SA0 bits of the control register DTMRcan be used to determine to which bus the bus access right should berequested. There are provided the contents of the source addressregister SAR for the data transfer channel corresponding to the startrequest. The DMAC 5 changes to state SA when the bus access rightacknowledge signal is active (busack_s=1) in response to the request forthe bus access right and the bus is detected to be ready. State SAoutputs the contents of the source address register SAR for the channelto a predetermined address bus and outputs a bus command to the bus.When the peripheral bus is accessed, for example, the peripheral buscontroller 24 activates the peripheral bus PBUS. When the access to theperipheral bus terminates, the peripheral bus ready signal becomesactive and is returned to the DMAC 5.

When detecting the active state (busrdy_s=1) of the bus ready signal forthe bus, the DMAC 5 changes to state SD. State SD stores read data inthe data buffer 35.

The DMAC 5 then changes to state DR. State DR requests the bus accessright to any of the buses predetermined to be the destination, i.e., theinternal bus IBUS, the peripheral bus PBUS, and the external bus EXBUS.There are provided the contents of the destination address register DARfor the data transfer channel corresponding to the start request. TheDMAC 5 changes to state DA when the bus access right acknowledge signalis active (busack_d=1) in response to the request for the bus accessright and the bus is detected to be ready.

State DA outputs the contents of the destination address register DARfor the channel to a predetermined address bus and outputs a bus commandto the bus. When the internal bus is accessed, for example, the internalbus controller 23 activates the internal bus. When the access to theinternal bus terminates, the internal bus ready signal becomes active(busrdy_d=1). When detecting that the bus is ready, the DMAC 5 changesto state DD.

Sate DD decrements the transfer count register TCR. Data in the databuffer 35 is output to the destination bus. When the bus ready signalbecomes active (busrdy_d=1), the DMAC 5 changes to state I to terminatethe operation of one data transfer.

FIG. 6 shows operation timing for the first example of using the DMAC 5.The first example represents data transfer between the input/outputinterface circuit 13 and the internal RAM 9.

The internal bus IBUS pipelines bus access right arbitration, output ofthe IAB (address bus of the internal bus IBUS), and input/output of theIDB (data bus of the internal bus IBUS). The bus state changes when busready signal ready-i for the internal bus IBUS is active or when busready signal ready-p for the peripheral bus PBUS is active. When ready-iis set to 1, the signal dmaack-i=1 or cpuack-i=1 grants the bus accessright to the bus master which then uses the IAB at the next clock andlater to output addresses. Addresses are used when ready-i is set to 1.The bus master that has been outputting addresses so far uses the IDB atthe next clock and later to input or output data.

The peripheral bus PBUS and the external bus EXBUS do not pipelineaddresses and data. Addresses are output during a 2-state period. Datais input and output at the second state of the address output. Theexternal bus EXBUS is capable of appropriately inserting waits andproviding predetermined accesses for interface with the associatedmemory.

In FIG. 6, state T1 activates data transfer start request signal dreqfor input/output interfaces to start the DMAC 5.

At state T2, the DMAC 5 activates dmareq-p (dmareq-p=1) to request thebus access right to the peripheral bus PBUS. Since the CPU 3 does notaccess the peripheral bus, the peripheral bus arbiter activates dmaack-p(dmaack-p=1) to grant the bus access right to the DMAC 5.

The DMAC 5 outputs an address to the peripheral bus PAB at state T3(DMAC:ra) and incorporates the contents of the peripheral bus PDB atstate T4 (DMAC:rd). The DMAC 5 reads a predetermined internal I/Oregister of the input/output interface circuit as well as a transferacknowledge signal (not shown) to inactivate the data transfer startrequest signal dreq.

At state T5, the DMAC 5 activates dmareq-i (dmareq-i=1) and requests thebus access right to the internal bus IBUS. Since a higher priority isgiven from the CPU 3, the internal bus arbiter 20 activates dmaack-i(dmaack-i=1) to grant the bus access right to the DMAC 5.

The DMAC 5 outputs addresses to the address bus IAB at state T6(DMAC:Wa) and outputs the read data to the data bus IDB at state T7(DMAC:wd).

As clearly understood from the operation timing in FIG. 6, the CPU 3transfers the bus access right to the DMAC 5 for one state and stopsoperations. The internal bus IBUS is used for only writing with respectto data transfer. Accordingly, it is possible to minimize an unnecessarywait state during which the internal bus IBUS is unavailable. Though notshown in the figure, almost the same operation takes place when data isread from the external bus and is transferred to the internal bus.

FIG. 7 is a timing chart for the second example of using the DMAC 5. Theexample here represents data transfer between the input/output interfacecircuit 13 and the SDRAM 28 connected to the external bus EXBUS.

The timing up to state T4 is the same as that in FIG. 6. At state T5,the DMAC 5 activates dmareq-ex (dmareq-ex=1) to request the bus accessright to the internal bus IBUS. Since a higher priority is given fromthe CPU 3, the internal bus arbiter 20 activates dmaack-ex (dmaack-ex=1)to grant the bus access right to the DMAC 5.

From state T6, the DMAC 5 outputs addresses to the external address busEXAB (address bus of the external bus EXBUS). For the SDRAM 28, the DMAC5 outputs row addresses at state T6 and column addresses at states T7and T8. Further at states T7 and T8, the DMAC 5 outputs the read data tothe EXDB. Meanwhile, state T7 inactivates the bus ready signal ready-ex(ready-ex=0) for the external bus EXBUS, allowing the state transitionof the DMAC 5 to wait. When there is a match between high-orderaddresses (row addresses) of the SDRAM 28 to be written, column addresscan be output at states T6 and T7 by omitting a state to output rowaddresses.

As clearly understood from the operation timing in FIG. 7, the CPU 3 canuse the internal bus IBUS also during data transfer by the DMAC 5 usingthe peripheral bus PBUS and the external bus EXBUS. This makes itpossible to minimize an unnecessary wait state.

FIG. 8 exemplifies a microcomputer system using the microcomputer 1 forprinter control. The printer control system comprises: the microcomputer1 whose input/output interface circuit 13 includes a send/receivecircuit (receive circuit or send/receive circuit) such as a universalserial bus; the buffer RAM (SDRAM) 28; character generation ROM (CGROM)41; program ROM 43: and a print control circuit 45. These components areconnected to a bus 47.

The address space of the microcomputer 1 is divided into predeterminedsizes. The program ROM 43 is connected to area 0. The buffer RAM 28 isconnected to area 1. The CGROM 41 is connected to area 2. The printcontrol circuit 45 is connected to area 3. A necessary portion of theexternally connected program ROM 43 is placed on the internal bus IBUSby storing it in the internal ROM 7, copying it to the internal RAM 9,or using internal cache memory. If the internal ROM 7 has a sufficientcapacity, the program ROM 43 can be eliminated.

The system further comprises a print head 49, a linefeed motor 51, and acarriage return motor 53. The motors 51 and 53 are controlled by outputsfrom the timer included in the peripheral function circuit 15. Thoughnot shown in the figure, the SCI included in the peripheral functioncircuit 15 is used for communication with a host. The A/D converter isused for supplying sensor information such as the number of sheets ofpaper, for example.

The microcomputer system in FIG. 8 allows the DMAC 5 to perform datatransfer between the input/output interface circuit 13 such as a USB andthe buffer RAM 28 without intermediation of the internal bus IBUS. TheDMAC 5 can output print data and pulse signals to drive the linefeedmotor 51 and the carriage return motor 52. Further, the DMAC 5 transfersdata sent to or received from the SCI. In these case, data istransferred between the peripheral function circuit 15 and the internalRAM 9.

Improving the integration of semiconductor integrated circuits canintegrate the print control circuit 45 and the like into themicrocomputer formed of a single semiconductor integrated circuit.Moreover, general-purpose memories such as the buffer RAM 28 can be alsointegrated into the microcomputer formed of a single semiconductorintegrated circuit. Memories such as the program ROM 43 and the CGROM 41may vary with microcomputer systems depending on different printermodels. It is preferable to use specific semiconductor integratedcircuits to configure such memories. All that is important is not tochange the logical bus configuration independently of which parts of thesystem should be integrated into a single semiconductor integratedcircuit.

The above-mentioned embodiments of the invention provide the followingeffects.

(1) The bus for the microcomputer 1 is separated from the other buses tocontrol them independently. The data transfer control in response to onedata transfer request allows the DMAC 5 to request the bus access rightin terms of the source and the destination independently. Operationssuch as reading programs from the memory 7 of the CPU 3 can beindependent of the data transfer, i.e., at least one of read and writeoperations using the other buses of the DMAC 5. This can improve themicrocomputer throughput.

(2) In response to one data transfer start request, the DMAC 5 requeststhe bus access right of one bus and the other bus, not using a sequenceof requesting the bus access right in response to different datatransfer requests for respective buses. It is possible to simplify ahandshake sequence of a data transfer request and its acknowledgment andcontribute to effective data processing by the DMAC 5 and the CPU 3.

(3) During a dual-address transfer, the DMAC 5 requests the bus accessright for reading and writing independently based on one start request.Consequently, the bus access right arbitration can occur frequently. Itis possible to shorten a wait from the time to request the bus accessright to the time to release it. Also in this respect, the dataprocessing performance can be improved.

(4) The bus controller 11 for the buses IBUS, PBUS, and EXBUS isprovided with the bus control logic corresponding to the access addressareas. This makes it possible to centrally control accesses from the CPU3 and the other bus masters and to minimize an increase in the logicalscale for the bus control.

(5) It is possible to concurrently execute programs on the CPU 3 usingthe internal bus IBUS and transfer data by the DMAC 5 using theperipheral bus PBUS and the external bus EXBUS, improving the dataprocessing performance of the microcomputer 1. When the SDRAM isconnected to the external bus EXBUS, the burst access can be appliedeasily. In other words, it becomes easy to allow the burst access to theSDRAM. Also in this respect, the data processing performance can beimproved.

While there have been described specific preferred embodiments of theinvention made by the inventors, it is to be distinctly understood thatthe present invention is not limited thereto but may be embodied invarious modifications without departing from the spirit and scope of theinvention.

For example, a data transfer device is not limited to the DMAC but maybe a data transfer controller or a coprocessor requesting the bus accessright. It is possible to appropriately change the DMAC transfer functionand the register configuration. Transfer data may be sized in blocks aswell as bytes, words, and long words. When a plurality of read and writeoperations is performed in response to one start request, it is justneeded to request the bus access right for each read or write operation.The number of bits in the address register is not limited to 32 and maybe changed in accordance with an address space for the CPU or thesemiconductor integrated circuit device. For example, a 16-megabyteaddress space may use 24 bits. It is also possible to change the numberof bits and the configuration of the transfer count register. Variousmodifications may be made to selections of transfer data sizes and startfactors depending on data to be transferred, I/O devices andinput/output interfaces functioning as transfer source and destination.

The microcomputer configuration is not limited to the above-mentionedembodiments either. The functional blocks can be modified variously. Inaddition to the DMAC, it may be preferable to include another datatransfer device such as a data transfer controller connected to thefirst bus (I bus) or the second bus (P bus).

Various modifications may be also made to specific configurations suchas those of the DMAC, the bus controller, the internal bus, and theexternal bus. There may be a plurality of peripheral buses or externalbuses. For example, it is possible to provide a plurality of secondbuses and to use one of them for direct connection between theinput/output interface and the DMAC. The external bus is not limited tothe interface between the semiconductor integrated circuit and theoutside. While there has been described the use of clocks of the sameoperating frequency on the internal bus, the peripheral bus, and theexternal bus, divided clocks may be used appropriately.

The microcomputer system can be used for not only printers, but alsodigital communication systems, digital media interface systems, and thelike. The microcomputer system further can be used for a system thatreceives data via the input/output interface, allows the DMAC totransfer the data to the buffer RAM via the DMAC, performs necessaryprocesses such as demodulation, error correction, and modulation, andallows the DMAC to transfer the data to the input/output interface fromthe buffer RAM for transmission. In this case, the DMAC is used for atransfer from the input/output interface to the buffer RAM and atransfer from the buffer RAM to the input/output interface. This enablesconcurrent processing with the remaining data processing by the CPU,improving the data processing performance.

While there has been described the invention made by the inventorschiefly with respect to its application to the single-chip microcomputeras the background field, the present invention is not limited thereto.The present invention is also applicable to the other semiconductorintegrated circuit devices such as those centered around a digitalsignal processor (DSP). The present invention can be applied toconditions capable of data transfer via at least two buses.

The following summarizes representative advantageous effects of theinvention disclosed in this application concerned.

It is possible to independently request the bus access right and outputaddresses to different buses, making it possible to solve the state ofcompeting for the bus access right among the buses. While the bus accessright of one bus is granted for reading or writing, the bus access rightof the other bus can be released. When the central processing unit isconnected to any of buses, releasing the bus access right by the datatransfer device enables data processing for the central processing unit.

In response to one data transfer start request, the bus access right isrequested for one bus and the other bus, not using a sequence ofrequesting the bus access right in response to different data transferrequests for respective buses. It is possible to simplify a handshakesequence of a data transfer request and its acknowledgment andcontribute to effective data processing by data transfer processing andthe central processing unit.

Consequently, it is possible to improve the efficiency of data transferprocessing and concurrent data processing by the central processingunit. That is to say, it is possible to perform processing mainly suchas reading programs by the central processing unit concurrently withdata transfer processing between various interface circuits and thebuffer memory. In addition, it is possible to improve the efficiency ofboth processing to be made concurrent with each other.

1. A semiconductor integrated circuit comprising: a first bus; a secondbus; a data transfer unit to transfer data between the first bus and thesecond bus; a central processing unit connected to the first bus; afirst module connected to the first bus; a second module connected tothe second bus; and a bus control unit controlling bus arbitration forthe first bus and the second bus, the data transfer unit requesting abus access right of one of the buses for reading to the bus controlunit, accessing the one bus for reading data, and releasing the busaccess right of the one bus, and requesting a bus access right of theother bus for writing to the bus control unit after releasing the busaccess right of the one bus and accessing the other bus for writing thedata in response to one data transfer start request, the centralprocessing unit being capable of bus access to the first module usingthe first bus in parallel with bus access to the second module using thesecond bus by the data transfer unit in response to one data transferstart request.
 2. The semiconductor integrated circuit according toclaim 1, wherein the bus control unit is capable of arbitration of busaccess right requests and bus control for the first bus and the secondbus independently in response to the one data transfer start request. 3.A semiconductor integrated circuit comprising: a first bus; a secondbus; a data transfer unit to transfer data between the first bus and thesecond buses; a central processing unit connected to the first bus; anda bus control unit controlling bus arbitration for the first bus and thesecond bus, the data transfer unit being capable of independentlyrequesting a bus access right and output an address to the first bus andthe second bus according to a data transfer start request, requesting abus access right of one of the buses for reading to the bus controlunit, accessing the one bus according to the bus access right of one busand releasing the bus access right of one bus, and requesting a busaccess right of the other bus for writing after accessing the one busfor reading, the bus control unit being capable of arbitration of busaccess right requests and bus control for the first bus and the secondbus independently in response to the one data transfer start request. 4.The semiconductor integrated circuit according to claim 3, wherein thecentral processing unit is capable of bus access to the first moduleusing the first bus in parallel with bus access to the second moduleusing the second bus by the data transfer unit in response to one datatransfer request.
 5. A semiconductor integrated circuit comprising: afirst bus; a second bus; a third bus; a central processing unitconnected to the first bus; program storage memory which stores acontrol program for the central processing unit and is connected to thefirst bus; a data transfer device capable of data transfer between thesecond bus and the third bus and a bus control unit for controlling thefirst bus, the second bus, and the third bus the data transfer devicebeing capable of independently requesting a bus access right and outputan address to the second bus and the third bus, requesting a bus accessright of one of the buses for reading, accessing to the one busaccording to the bus access right, and releasing the bus access right ofone bus, and requests a bus access right of the other bus for writing inresponse to one data transfer start request, the bus control unit beingcapable of arbitration of bus access right requests and bus control forthe first bus, the second bus, and the third bus independently.
 6. Thesemiconductor integrated circuit according to claim 5, wherein thecentral processing unit can access the second bus or the third bus fromthe first bus via the bus control unit.
 7. The semiconductor integratedcircuit according to claim 5, wherein the data transfer device has aplurality of data transfer channels and a control register to specifydata transfer channel operations, and wherein the control register has atransfer request generation source specification area for definingcorrespondence between a data transfer channel to receive a transferrequest and a transfer request generation source; a source busspecification area for defining correspondence between a data transferchannel and a transfer source bus; and a destination bus specificationarea for defining correspondence between a data transfer channel and atransfer destination bus.
 8. The semiconductor integrated circuitaccording to claim 7, wherein a central processing unit can access thecontrol register.